Ангела 🌙added a note hace 3 años

We can't replace "who" with "that" when we speak about details we can neglect. In that part of a sentence, we should use "who". This part is called a non-defining relative clause. It's separated by commas:
It was Sheila, who was planting flowers.
We use "that" in a defining relative clause; it is not separated by commas. We use defining RC when we mention important details. For instance:
Sheila has a beautiful garden that she waters every weekend. It's easy to remember: if there are no commas, we can use "that". If there are, there's no more place for "that", we can't use it anymore.
This topic is called Relative Clauses. This topic is rather essential, so I'd recommend thoroughly studying it :)

Incorrect! It was Sheila who was planting flowers. [no comma]

Correct: The detective spoke to Sheila, who was planting flowers at the time. [comma]

Angela, there's nobody on this site to help you with English. Don't learn English from Russians or any other non-native nationality. There are too many native English speakers in the world to waste your time here.

Uly, can you advise any native speaker to practice with ? I can help with Russian in my turn

Do you have Telegram?

Yes. I do. Why?

K. I sent u a message